The invention relates to silicon integrated circuit technology, and, more particularly, to an anisotropic etch process using Cl2/He chemistry in the manufacture of a silicon integrated circuit device.
Etching processes are often employed in the manufacture of silicon integrated circuit devices.
Silicon integrated circuit manufacturing processes typically begin with a single-crystal silicon (Si) workpiece. The workpiece is subjected to a series of steps carried out in a particular order. Those steps serve to appropriately layer and configure the wafer workpiece with desired semiconductor pathways to create a useable integrated circuit device. The ordering of the steps, and the parameters for those steps, dictate the resulting integrated semiconductor circuitry achieved from the manufacturing process.
The term xe2x80x9cetchingxe2x80x9d describes a variety of techniques by which material is removed uniformly, or in the delineation of a pattern, from a wafer during manufacture of a silicon integrated circuit device. Etching is often a step or steps in the manufacturing process. Etching steps serve both to xe2x80x9ccleanxe2x80x9d the surface of a wafer to remove defects and/or foreign debris and to shape or xe2x80x9cprofilexe2x80x9d the wafer as appropriate for the manufacturing process. In any case, the goal in etching is removal of portions of material from a wafer as desired for the particular application.
There are several types or classifications of etching processes. Of these different types or classifications, there has been no single type or classification of etch which is best or preferred in all circumstances. Typically, a particular type or classification of etch is only suitable for a particular application or class of applications. It would be an improvement in the technology if an etch process were developed that exhibits favorable aspects in several or a number of varied applications.
The first category of types or classifications of etching processes deals with the particular etchant which effects the etch, i.e., the medium which causes the removal. Generally, there are two types of etchants: chemical and physical. In the case of chemical etchants, a chemical is used to dissolve or react with materials of the wafer to be etched away. Chemical etching may occur by any of several different processes. The simplest process is dissolution of a material to be etched from the wafer in a solvent without any change in the chemical nature of the dissolved material. Other chemical etching processes involve one or more chemical reactions in which the product formed from the reaction is soluble in the etching medium or may be carried away from the surface by the medium. Various types of reactions which may be involved are oxidation-reduction, complexation, and vaporization. In these processes, the parameters of the etching steps, such as temperature and pressure in which the process occurs, may be important factors to the success of the etch.
The second type of etchants are physical etchants. In physical etching processes, material is selectively removed from the wafer by momentum transfer from a rapidly moving inert projectile. Ion milling is one form of physical etching. Another form of physical etching is sputtering. Both of these techniques require the formation of a gas discharge producing high-velocity ions. The high-velocity ions bombard the wafer in selective locations causing removal of desired materials from the wafer. These processes are referred to as plasma-assisted processes because characteristics of the particular gas discharge may be important to the etch outcome.
Etching processes are also typed or classified by the degree of anisotrophy of the etch. Anisotropic etching occurs in a single direction, whereas isotropic (the opposite of anisotrophic) etching occurs in all directions. Typically, in an etch, amorphous materials of uniform composition will be etched isotropically, whereas many crystalline materials will be etched both isotropically and anisotrophically. The degree of anisotrophy of etching usually will depend upon the crystallographic orientation of the material being etched and the particular etching reagent used. Where a polishing action is desired from the etch, isotropic etching is preferred to achieve a structureless, or smooth, surface. If structural shaping is the objective of the etch, however, anisotropic conditions are preferred. The degree of anisotrophy of an etch depends on a variety of parameters, such as the particular etchant, the temperature, the pressure, the selectivity of the etchant for particular materials of the wafer, and others.
Etching processes may be even further typed or classified as wet or dry etchings. In wet etching processes, etching takes place in a liquid. In dry etching processes, etching takes place in a gas. A variety of factors impact wet or dry etching processes, such as the particular liquid or gas medium, temperatures, processes, and other factors.
Selectivity of etching processes is another factor important in classifying or typing etch processes. Selectivity, in fact, is one of the most important factors affecting the effectiveness of and outcome of an etching process. Selectivity refers to differences in etch rates between different materials, or between compositional or structural variations of the same materials. Most etching processes must be controllably selective because the material to be etched is usually part of, or in close proximity or relationship with, a wafer that consists of several material components. Selectivity in etching depends upon a number of factors, such as choice of etching technique, etchant composition, temperatures, pressures, and constraints of the system and materials etched.
The foregoing types or classifications of etching processes are not absolute, as many etching processes may include combinations and variations on the categories. Nevertheless, the presently most used etching processes can be generally classified by reference to these various categories. Because each category has particular advantages/disadvantages and characteristics in particular applications, it would be beneficial to have an etching process which works effectively in a variety of conditions and applications.
In the manufacture of silicon integrated circuit devices by the aforesaid etching processes and other manufacturing techniques, there often occurs an undesired result: The actual geographic configuration of the product device differs from the design geographic configuration. This discrepancy between actual and design is many times the result of inaccuracies and ineffectiveness of etching processes in delivering desired results. As previously described, there can be numerous factors important to the result obtained from an etching process, including for example, anisotropy of the etch, inability of equipment to maintain optimum conditions of sterility and tolerance, pressures, temperatures, chemistry of etchant compositions, and others. These factors and others may result in dimensional and compositional changes in the actual device from the design device. Those changes can lead to functional and operational problems. Designers and manufacturers of silicon integrated circuit devices must understand that these changes in dimensions will occur in an etch and must compensate therefor in the design and manufacturing process. Of course, it is preferable to limit the possibility of these changes whenever possible. Those who practice the art, therefore, continually search for still better and improved methods to maintain desired wafer geographic configuration or xe2x80x9cprofilesxe2x80x9d and other aspects of wafer quality.
The present invention provides for an improved etching process which has, in tests, proven to be particularly effective in substantially maintaining desired profiles upon etching. Further, the etch process has proven to substantially improve characteristics of the etch, such as selectively and anisotrophy. Even further, the present etch process provides these improvements and yet maintains generally desirable characteristics of etch processes, for example, etch rate and other conditions necessary for a commercially useable etch process.
According to an aspect of the invention, a method of manufacturing a silicon integrated circuit device is provided, comprising etching an ONO layer with Cl2/He chemistry. According to a further aspect of the invention, the method may further comprise the step of depositing the ONO layer. The method may also further comprise the step of etching a portion of said ONO layer with Cl2/He chemistry.
According to a further aspect of the invention, an ONO etch process is provided, comprising of: etching an ONO layer disposed upon a silicon wafer with a plasma at a first power, the plasma including chlorine and helium atoms, the ONO layer comprising a top silicon dioxide layer, a nitride layer, and a bottom silicon dioxide layer; etching the nitride layer with the plasma at a second power that is substantially less than the first power after breaking through the top silicon dioxide layer; and, stopping further plasma etching after reaching the bottom silicon dioxide layer.
The invention offers distinct advantages over the prior art. For example, critical dimension control is improved, profile control is improved, and residual silicon dioxide thickness after the etch is more uniform in thickness due to the high selectivity of the Cl2/He chemistry. The improved profile control contributes to reduced bird""s beak oxidation. These and other advantages of the invention are apparent from the detailed description that follows.